The cylinder device converts relative rotational motion between a screw shaft and a screw nut to linear motion, and hence linearly drives mechanism parts, or the like, that are connected to the screw shaft or to the screw nut. According to the type of a motor that rotationally drives the screw shaft and the screw nut, the cylinder device is classified into an electric, a hydraulic, and a pneumatic cylinder device. In particular, the electric cylinder device causes noise less frequently and can be more easily handled without causing oil leakage or the like than the hydraulic and pneumatic cylinder devices, and therefore the electric cylinder device is widely used in various pieces of industrial equipment. Therefore, conventionally, the electric cylinder device has been actively researched and developed, and many inventions or contrivances relative to the electric cylinder device have already been disclosed.
For example, Patent Literature 1 discloses an invention whose title is “Electric Cylinder” and that relates to a cylinder device for use in, for example, an injection molding apparatus.
The cylinder device disclosed in Patent Literature 1 is composed of a motor disposed in parallel with a screw shaft, a train of gears that transmit a rotational driving force of the motor to the screw shaft, a nut that meshes with the screw shaft, a hollow rod that restrains the rotation of the nut, and an outer cylinder into which the rod is slidably fitted.
According to the thus formed structure, the following operation is performed. When the rotation of the motor is transmitted to the screw shaft by the train of gears, the nut and the rod linearly move, and the rod expands and contracts.